Among female athletes, the only one to emerge in the standings is the U.S. tennis player Serena Williams, with 25.7 million euros per year and a distant 63rd among the 100 published.
The top 100 includes athletes from 25 countries and their $4bn (£3,1bn) combined earnings are up 5% from the previous year, when Mayweather was first with $285m (£224m).
Messi is only the second footballer to top the rankings after Ronaldo, and only the eighth different athlete to take the number one spot since the rankings began in 1990.
Brazil and Paris Saint-Germain striker Neymar completed a sweep of the top three positions by footballers, coming in third with earnings of $105 million.
However, McGregor not only kept his status as the highest earner from the sport of mixed martial arts, he was also the only MMA fighter to make it into the Top 100.
Manchester United's Paul Pogba is the highest earning Premier League player in 44th place with $49.8 million.
Boxer Saul "Canelo" Alvarez was the highest-earning non-footballer on the 2019 list, with $94m in total - just $2m of which were through endorsements, meaning he had the same salary as Messi.
Evergreen tennis star Roger Federer was fifth on the list with total earnings of $93.4m. Aaron Rodgers (NFL player) $134 million 8.
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